Turbocharged and supercharged engines may be configured to compress ambient air entering the engine in order to increase power. Compression of the air may cause an increase in air temperature, thus, a charge air cooler (CAC) may be utilized to cool the heated air thereby increasing its density and further increasing the potential power of the engine. Condensate may form in the CAC when the ambient air temperature decreases, or during humid or rainy weather conditions, where the intake air is cooled below the water dew point. Condensate may collect at the bottom of the CAC, or in the internal passages, and cooling turbulators. When torque is increased, such as during acceleration, increased mass air flow may strip the condensate from the CAC, drawing it into the engine and increasing the likelihood of engine misfire and combustion instability.
One approach to address condensate formation in the CAC may involve using warm or heated intake air. Heated intake air may increase the temperature of the charge air entering the CAC. By increasing the charge air temperature at the CAC inlet, the air traveling through the CAC may be further away from the condensation point, reducing the amount of condensation and engine misfire. However, warmer intake air may increase the temperature of the air entering the engine intake manifold and result in increased knock during warmer engine operating conditions.
In one example, this apparent paradox may be addressed by a method for adjusting a fresh air source position of intake air responsive to a condition of a charge air cooler. For example, by adjusting the position of an induction valve, warmer air or cooler air may be drawn into the induction system. The adjusting may be responsive to operating conditions in order to concurrently address warm-up operation, condensate formation, and potential for engine knock. For example, when an amount of condensate in the CAC is above a threshold level and/or engine temperature is below a threshold temperature, the induction valve may be adjusted into a first position to draw in warm intake air. In another example, when spark timing is within a threshold of a borderline knock limit, the induction valve may be adjusted into a second position to draw in cooler intake air.
In this way, fuel economy losses and condensate formation in the CAC may be reduced. For example, in response to increased condensate formation, warmer intake air may be used to increase the temperature of the air entering the CAC. Thus, the air traveling through the CAC may be further away from the condensation point, reducing the amount of condensate that forms. Additionally, in response to a lower engine temperature, warmer intake air may be used to accelerate engine warm-up during a cold start (e.g., increase engine temperature) and reduce pumping losses. By reducing pumping losses, fuel economy may be increased. Warmer intake air may also increase the temperature of an intake throttle body, reducing throttle body icing. Alternatively, in response to an engine knock indication, cooler intake air may be used to adjust a borderline knock limit. The engine knock indication may include whether spark timing is within a threshold of a borderline limit. When spark retard nears the borderline knock limit, fuel economy losses may increase. Thus, cooler intake air may reduce these losses and increase fuel economy.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.